"Infrastructure Management Servers cannot be accessed" seen when viewing TSPS console -> Monitoring -> Events -> Showing events from all Infrastructure Management Servers
Check to see if this error is present when logged into the TSPS as the admin user. If not, then it might be a permissions issue.
If you're seeing the error with the admin user, check if the TSIM is showing as Connected in the Components screen.
Another test is to confirm whether the TSPS HA has been setup correctly. There should be an ha.master.node file in the 'ha' directory on the primary server and a corresponding ha.standby.node file on the secondary server. Also check that the ha.conf file on the secondary server has the same order as seen on the primary server. If the TSIMAudit.log shows CONNECTED to the dormant TSPS, then this might indicate an HA configuration problem with the TSPSs.